Pesticide Mode of Action Shelley Mills Valley County Extension Agent

What is a pesticide?

Pesticides Insecticides Acaricides Herbicides Chemosterilants Fungicides Virucides Rodenticides Algicides Miticides Nematicides Avicides Piscicides Molluscicide Bactericides

Mode of Action Where and how the pesticide works within the organism.

Insecticides IGR – Insect Growth Regulators Methoprene, NEEM oil, Pyriproxifen

Central nervous system disruptors Neonicitinoids (neonics) Imidacloprid – Gaucho, Advocate, Admire Thiamethoxam – Platinum, Cruiser Clothianidin – Poncho, Dantop Thiacloprid - Calypso Organophosphates Malathion Parathion Carbamates Carbaryl - Sevin

Neonicitinoids (neonics) Acetylcholine is a neurotransmitter – sends signals to other cells Neonicotinoids (neonics) like imidacloprid irreversibly bind to the nicotinic aceytlcholine receptors and block them in the open position causing constant neuromuscular stimulation. Acytlcholinesterase is an endogenous enzyme that under normal conditions breaks down the acetylcholine and stops the stimulation, but it cannot break down neonics - so the process is irreversible. Insects are much more susceptible than humans and other mammals to this binding.

Ogranophosphates and Carbamates Organophosphates interfere with the production of acetylcholinesterase the enzyme that stops the overstimulation of the nerves.

Pyrethroids Pyrethroids and DDT interact with the sodium pump that is necessary to produce acytelcholine. This in turn stops the firing of the neurons by causing the cell to be unable to repolarize. The membrane becomes permanently depolarized and ultimately leads to paralysis.

Pheremones Sex attractants Aggregation pheromones Repellants Pheromones usually have limited use because their range of influence is much smaller and they are very difficult to reproduce from nature

Rodenticides Anticoagulant Wafarins and coumarins functions as an anitvitamin and competes with vitamin K uptake in the liver. (reversible)

Rodenticides Acute single dose products Aluminum phosphide (burrow) Zinc Phosphide (gut) Aluminum phosphide and zinc phosphide kill by converting to phosgene gas in the presence of moisture. In the gut or in the burrow.

Herbicides Group 1 ACCase inhibitor – fop’s, dim’s and den’s – acetyl CoAcarboxylase inhibitor (membrane synthesis) Clodinafop-P Discover Fenoxaprop-P Puma , Tacoma, Parity Fluazifop-P Fusilade DX Quizalofop Assure II, Targa Clethodim Select, Trigger, Volunteer Intensity Sethoxydim Poast Pinoxaden Axial XL Usually used for post emergence grassy weed control BLW have a less sensitive ACCase enzyme Acetyl co enzyme A carboxylase inhibitor and affects fatty acid that is important in membrane synthesis. Many broadleaved species are more resistant to group 1 because they have a less sensitive ACCase enzyme

Symptoms = yellowing of young leaves purpling of older leaves Symptoms = yellowing of young leaves purpling of older leaves. Affects growing point

Herbicides Group 2 ALS inhibitors – Imi’s, SU’s, TPS’s, SACT’s – branched chain amino acid disruption Imidazolinones - Assert, Beyond, Arsenal Pursuit Sulfonyl Ureas – Glean, Telar, Escort, Ally Oust, Harmony, Finesse, Matrix Triazolopyrimidine – First Rate, PowerFlex Sulfonylamino-carbonyltriasonlinone – Everest, Olympus and Varro Broad spectrum contol – usually at low rates, soil applied or post-emergent Acetolactate synthase interupts the formation of branched-chain amino acids Symptoms are latent – usually chlorosis first with purple underleaves, growing points are affected can cause stunting and shortened internodes.

Axillary leaf bud growth and chlorosis of the new growth

Herbicides Group 3 Mitotic inhibitor Dinitroaniline – Sonalan, Prowl and Treflan Inhibit cell division Generally applied pre-emergent, absorbed by roots and shoots but don’t translocate much so you will see stubby, shortened roots and thickened, stubby shoots.

Stubby roots and thickened and shortened shoots.

Herbicides Group 4 Growth Regulators – synthetic auxins Benzoic Acids - Banvel, Clarity, Rifle Pyridines - Milestone, Clopyralid (Stinger, transline), Tordon, Starane, Clean Slate Quinoline – Facet, Quinstar, Phenoxy’s – 2,4-D amine and ester, MCPA, Symptoms are leaf twisting and curling (generally upward leaf curl) stem elongation, epinasty, stunting and yellowing.

Herbicides group 5, 6 & 7 Photosystem II disruptors PSI (5) - Atrazine, Princep metribuzen, Sencor PSII (6) – Bromoxynil, Basagran PSII (7) – Diuron, Linuron, Spike (soil sterilants) Disrupt photosynthesis resulting in bleaching of plant. Symptoms appear in the presence of sunlight. PSI and PSII herbicides are like rapid cancer agents, destroying tissues right and left. Very destructive.

Bromoxynil & Traizine

Herbicides Group 9 EPSP Synthase Inhibitor Glyphosate Disrupts aromatic amino acid production (used to make proteins) which are used extensively throughout the plant Chlorosis after 7 to 10 days – then characteristic orange-yellow color. Symptoms appear much slower in cold weather and lower use rates. Affects the Shikimate pathway

Other herbicides that you may hear about (14) PPO (Protox) Inhibitor – Sharpen, Vida, Aim (22) PSI (Photosystem I inhibitor) – Paraquat, Diquat (31) CHT PPO – PSI symptoms appear rapidly within 1 to 2 hours after application CHT – Cold, Hard, Steel

Contact VS Translocated

Herbicide Resistance Group 1, Group 2 and Group 9 Kochia – 2, 9, 4, 2+9, Wild Oats – 1, 2, 8 (2 different sites), 1+2 Russian Thistle – 2 Green Foxtail – 1 Horseweed – 9 http://weedscience.org/details/usstate.aspx ?StateID=27